Titanium nitride (TiN) coatings were obtained on the surface of 12Kh18N10T steel by air plasma spraying (APS) of TiN powders using an arc plasmatron made by the authors. The plasmatron has a node of circular input and gas-dynamic focusing of the powder and the output apertures of the nozzle-anode are made in the form of rectangular narrowing-expanding channels (No.34334 RK: IPC H05H 1/42). A study of operation modes of a plasmatron for spraying of powder coatings was carried out. The structural-phase state, microhardness and wear resistance of TiN coatings were systematically investigated. The optimum APS operating mode for deposition of TiN powder was determined: current 250 A, voltage 68 V, argon gas flow 34 L/min, spraying distance 150 mm. To reduce the oxidation of TiN powder in the APS process, a method of creating a nitrogen environment at the outlet of the anode nozzle, nitrogen flow rate 2.3 bar was used. The results of structural analysis showed that TiN is the main phase of the coating. The mechanism of formation of TiN structures was characterized by analyzing SEM results of TiN coating surface morphology and TiN droplets sprayed on the surface of the sample. The results showed that the TiN(1) coating has better wear resistance than the TiN(2) and TiN(3) coatings. The cross-sectional and longitudinal microhardness of the TiN coating was investigated. The highest cross-sectional hardness of TiN coating is 1250 HV0.1, which is in accordance with mode 1.

This paper examines the influence of electrolyte-plasma surface hardening on the structure and microhardness of wheel steel mark 2. In the work electrolyte-plasma surface hardening was carried out in an electrolyte made from an aqueous solution 10 % carbamide (NH2)2CO 20 % sodium carbonate Na2CO3. The processing time was 2 seconds, Tmax = 850–900 ºC; U= 320V; I=40A. According to the results of the scanning transmission electron microscopy, the electrolyte-plasma surface hardening caused a change in the morphological constituents of mark 2 steel. In the initial state, the matrix of steel is a α-phase, the morphological components of which are fragmented ferrite, unfragmented ferrite and pearlite. After electrolytic-plasma surface hardening, a batch, high-temperature plate and low-temperature plate martensit is formed on the surface of the sample. Investigations have been carried out on microhardness determination on cross-section of wheel steel samples after quenching in aqueous solution of electrolyte. It is found that after electrolytic-plasma surface hardening, the microhardening values of this hardened surface layer increased ~ 3 times compared to the steel matrix, and the thickness of the hardened layer is 1000–1500 microns.